The manufacture of articles that include thermoplastic structures useful to, e.g., fasten articles together (hook and loop systems, capped stems, etc.) are known. Such processes, however, typically provide thermoplastic structures that are located over an entire substrate or web. Where smaller, discrete regions of fastening or other structures are required, pieces of the preformed thermoplastic structures are often attached to a separate article, e.g., the fastening tab of a diaper or incontinence garment.
The handling and attachment of such discrete pieces can, however, be problematic, by potentially reducing throughput, causing waste (where the discrete pieces are not securely attached), etc. The discrete pieces may also present relatively sharp edges that may be the source of irritation or discomfort.
Some of these issues are addressed in U.S. patent application Ser. No. 09/257,447 by Tuman et al., filed on Feb. 25, 1999, titled WEB HAVING DISCRETE STEM REGIONS (also published as International Publication No. WO 00/50229). That document describes webs having discrete polymeric regions formed thereon by the use of extrusion coating (with or without the use of rotating blades). The extrusion coating may be performed using a series of nozzles that may be cycled to deliver discrete amounts of polymeric material to a web. Another alternative method discussed in the document is the use of screen printing.
All of the methods for forming discrete polymeric regions disclosed by WO 00/50229 include some disadvantages. For example, the use of extrusion dies and/or nozzles and any associated equipment (e.g., rotating blades, etc.) may result in limited shapes that can be formed on the webs. Another potential disadvantage is that the speed at which the patterns may be formed is somewhat limited, especially where larger or thicker discrete polymeric regions are required. Another disadvantage associated with extrusion-based systems is that the ability to form some shapes with any precision may be limited by the nature of the extrusion process.
As for the use of screen printing to form discrete polymeric regions, one disadvantage is that the amount of material that can be delivered through the orifices of a screen may not be sufficient to allow for forming of structures after deposition of the discrete polymeric regions, particularly when the thermoplastic compositions used for the discrete polymeric regions have a relatively high viscosity. More importantly, however, may be the limitations on screen orifice size. If the orifices are too large, the integrity of the screen can be impaired, particularly if higher pressures are required to force higher viscosity materials through the screen orifices.
Another disadvantage related to screen orifices is that orifices that extend continuously about the circumference of the screen printing roll cannot be provided without destroying the integrity of the roll. Further, orifices that extend too far in any direction can significantly limit the forces that can be applied to the screen printing roll without excessive distortion of the screen printing roll.
Another disadvantage of screen printing processes is that the ability to force the molten thermoplastic composition into the substrate (where, e.g., the substrate is porous, fibrous, etc.) may be limited because no physical structure is provided directly opposite from the substrate on which the discrete polymeric regions are deposited.
Screen integrity may also limit the amount of pressure that can be applied to clean the screen of the molten thermoplastic composition between printing passes. As the thermoplastic material builds up on the screen, it may be subject to charring or other degradation that could further hamper performance of the system as a whole.